Abstract
The purpose of this work is to present the development of low-manganese pipes containing 1% Cr and Boron manufactured by the HF-ERW process according to standard API SPEC 5CT (2011) L80 grade. The study has an innovative character and the main competitive advantage is the relatively low cost of manufacturing combined with the high level of quality in welding process and subsequent heat treatment of quenching and tempering.
The chemical composition of the steel was designed in such a way to ensure good weldability, high hardenability and low mechanical properties variation after tempering. Low levels of Manganese was established and increase the resistance of hydrogen induced cracking due the tendency of formation of MnS inclusions in the continuous casting. Additionally, levels of 1%Cr were incorporated to ensure corrosion resistance in water injection wells. Hollomon model was used to set the tempering temperature as a function of the aim mechanical property. To characterize the tube, the follow tests were performed, tensile, Charpy, hardness, microhardness, optical microscopy, SEM and CO2 corrosion tests.
The seam weld presented excellent results under UT inspection. The low variability in the mechanical properties shows that the quench and tempering process was stable, which is able to meet the API SPEC 5CT (2011) L80 grade and NACE MR0175 (2003). The scanning electron microscopy identified fine precipitates dispersed in a martensitic matrix, this being the mechanism of secondary hardening which raised the tempering temperature as provided by Hollomon model. The corrosion resistance was compared with N80 and confirmed more than 75% resistance according to the references.
In view of the results we conclude that the low manganese tube containing 1%Cr manufactured by the process HF-ERW meets the requirements of Standard API SPEC 5CT (2011) L80 grade and thereby contribute significantly in increasing competitiveness in the oil and gas production, mainly for the water injection wells by increasing corrosion resistance and offering a tube manufactured by a competitive process compared to seamless.
